Dielectric fluid composition containing vegetable oils and free of antioxidants

ABSTRACT

A dielectric fluid composition containing of 60% to 63% in weight of mono-unsaturated fatty acid, of 20% to 23% in weight of di-unsaturated fatty acid, of 5% to 7% in weight of tri-unsaturated fatty acid, and of 6% to 8% in weight of saturated fatty acid, such that the dielectric fluid is free of antioxidants and/or external additives and has the following properties: a dielectric strength of 40 kV to 70 kV at a separation of 2 mm, a dielectric constant of 2.5 to 3.1 at 25° C., and a dissipation factor of 0.05% to 0.15% at 25° C. The dielectric fluid composition can be obtained by a combination of 95.5% to 99.25% in weight of at least one high oleic vegetable oil, of 0.25% to 1.5% in weight of grape seed oil, of 0.25% to 1.5% in weight of sesame seed oil, and of 0.25% to 1.5% in weight of rice bran oil.

TECHNICAL FIELD OF THE INVENTION

The current invention is related in general to dielectric fluids forapparatus used in the transmission and distribution of electric energy.More specifically, the invention relates to dielectric fluids comprisingrelatively pure mixtures of vegetable oils and free of externalantioxidant compounds.

BACKGROUND OF THE INVENTION

Electrical equipment such as transformers, reactors, capacitors, circuitbreakers, among others, use internally dielectric fluids, also known asdielectric oils, which are used as an insulation and dissipation meansof heat generated by the internal components of the apparatus.

The dielectric fluid must be able to perform its functions effectivelyand reliable as a cooling and insulation means during the service lifeof the electric apparatus.

Obviously, many of the properties of the dielectric fluid should beconsidered as necessary to provide the expected cooling and dielectriccapacity, according to its application, therefore, depending on them itsability to function effectively and reliably may be affected. Theseproperties may include: dielectric strength, dielectric constant,dissipation factor, viscosity, acid number, pour point temperature andignition temperature.

The dielectric strength of the fluid shows its ability to resistelectric breaks at certain frequencies of electrical power and it ismeasured as the minimum electric voltage required to cause the formationof an arc between two electrodes submerged in the dielectric fluid.

The dielectric constant is the ratio of capacitance of a capacitor witha dielectric (oil) between its plates, and the capacitance of saidcapacitor where the dielectric is a vacuum. This property is related tothe ability of the dielectric fluid to conduct electricity, so that at alower ability value the capacity of the dielectric fluid will increase.

The dissipation factor of a dielectric fluid is the measurement ofdielectric losses in this fluid, usually in the form of heat. A lowdissipation factor indicates low dielectric losses and a lowconcentration of polar soluble contaminants in the dielectric fluid.

The acid number in a dielectric fluid is a measure of the constituentsor acidic contaminants of the fluid. The acidity of a dielectric fluidis due to the formation of acid oxidation products. Acids and otheroxidation products, together with water and solid contaminants affectthe dielectric properties and other properties of the dielectric fluid.The rate of increase in acid number of the dielectric fluid is a goodindicator of the rate of aging of said fluid.

Pour point temperature is the temperature at which a fluid flow stops,converting into a solid state under environmental pressure conditions.The pour point temperature can also be defined as the maximumtemperature (usually below zero Centigrades) for which the dielectricfluid cannot move or deform with its own weight. The lower thistemperature, the easier this dielectric fluid shall be applicable inelectrical apparatuses subject to extreme low temperatures below zero °C.

The ignition temperature, also known as flash point, is that temperaturethe dielectric fluid must reach to result in the ignition of vapors fromsaid fluid, when exposing them to the air and to the source of ignition.

As dielectric fluids cool off by convection, the electrical equipmentwhere they are applied, the viscosity of these fluids at differenttemperatures is another important factor to be considered. The viscosityis a measure of the strength of a fluid to flow it is typically analyzedin terms of kinematic viscosity. At low viscosities, the dielectricfluid circulates or flows better inside the appliance and thus allowsbetter heat dissipation.

Among the dielectric fluids used in electric apparatuses and havingthese and other properties, those dielectric fluids are included basedon mineral oils, silicones, synthetic oils, vegetable oils withantioxidants or mixtures thereof.

Dielectric fluids based on mineral oils derived from petroleum,silicone-based oils or synthetic oils have been widely used inelectrical transformers, transmission cables and capacitors. Examples ofthese oils are found in U.S. Pat. Nos. 4,082,866, 4,206,066, 4,621,302,5,017,733, 5,250,750, and U.S. Pat. No. 5,336,847.

Although these dielectric fluids show a good performance as aninsulating means and heat dissipation when used in electricalapparatuses, they present a high risk of contaminating the environment,when an accident occurs in which the fluid is spilled, because theycontain synthetic elements, which are considered toxic and notbiodegradable.

These disadvantages, as well as global environmental trends haveresulted in the establishment of more stringent governmental andenvironmental regulations, requiring the industry to offer ecologicproducts, that is, products with low impact to the environment.

In response to the former problem, the dielectric fluids based onmineral oils, silicone-based or synthetic, a recently exploredalternative is the development of dielectric fluids based on edible oilseeds, that may be seeds of soybean, sunflower, safflower, rapeseed,castor, linseed, cotton, rice, corn, olives and grapes.

It is well known that vegetable oils are deficient in terms of theirproperty of stability to oxidation, that is, react easily with oxygenfavoring degradation of the fluid, unlike the type of dielectricmineral, silicone or synthetic oils.

Recently, it has been shown that it is possible to optimize theoxidative properties of dielectric fluids based on edible seeds throughchanges in the manufacturing processes of the oil, or through theincorporation of synthetic compounds that have the primary role ofslowing reactions with the oxygen, and thus, facilitating their use inelectrical apparatuses such as transformers. Some of the solutions ofvegetable oil dielectrics are described in patent documents GB-609133,CA-2204273, U.S. Pat. Nos. 5,766,517, 5,949,017, 5,958,851, 6,037,537,6,159,913, 6,184,459, 6,207,626, 6,245,726, 6,274,067, 6,280,659,6,312,623, 6,340,658, 6,347,033, 6,352,655, 6,398,986, 6,485,659,6,645,404, 6,726,857, 6,905,638, and U.S. Pat. No. 7,048,875.

Some of the vegetable dielectric oils that have been developed presentin their compound a high content of oleic acid in order to strengthenthe oxidative capacity of the oil, as described in U.S. Pat. Nos.5,949,017, 6,274,067, 6,312,623, 6,645,404, and U.S. Pat. No. 7,048,875.However, like other vegetable dielectric fluids they incorporateantioxidants to their compound, and other synthetic additives to improvethis property, as well as other characteristics of the oil.

It has been shown that the addition of antioxidants or syntheticadditives to the current vegetable dielectric oils compensates for poorstability to natural oxidation within these fluids, however, from theecological point of view this is not desirable, since the chemicalcomposition of these additives may reduce the ability of biodegradationof the oil, besides damaging its non-toxic characteristic, it is knownthat some of these synthetic compounds present toxic characteristics.

Therefore, there is a clear need to provide a dielectric fluid fromvegetable oils with suitable characteristics, not only in performancefor its use in electrical apparatuses, but also in environmental issuesthrough the incorporation of zero synthetic additives or externalantioxidants in its composition.

SUMMARY OF THE INVENTION

Referring to the aforementioned and with the aim of finding a solutionto the constraints encountered, it is the object of the invention toprovide a vegetable dielectric fluid composition comprising of 60% to80% in weight of mono-unsaturated fatty acid; of 2% to 23% in weight ofdi-unsaturated fatty acid; of 0.5% to 7% in weight of tri-unsaturatedfatty acid; and of 5% to 8% in weight of saturated fatty acid, whereinsaid dielectric fluid is free of external antioxidant compounds and hasthe properties of a dielectric strength of 40 kV to 70 kV at aseparation of 2 mm, a dielectric constant of 2.5 to 3.1 at 25° C., adissipation factor of 0.05% to 0.15% at 25° C., a viscosity less than 50cSt at 40° C., an acid number less than 0.06 mg KOH/g, a pour pointtemperature of at least −18° C., and an ignition temperature over 300°C.

Another object of the invention is to provide a dielectric fluidcomposition comprising a vegetable mixture of 95.5% to 99.25% in weightof at least a high oleic vegetable oil; of 0.25% to 1.5% in weight ofgrape seed oil; of 0.25% to 1.5% in weight of sesame seed oil, and of0.25% to 1.5% in weight of rice bran oil.

Another object of the invention is to provide a method for producing adielectric fluid free of antioxidants and/or external additives; themethod consists of the following steps: mixing two or more crudevegetable oils, removing hydrophibic phospholipids and non-hydrophobicsfrom the mixture of vegetable oils, by adding food grade citric acidwithin a temperature-controlled reactor; distilling under high vacuumthe mixture of vegetable oils to remove free fatty acids present;removing impurities from the mixture of vegetable oil, shaking it undera direct dry steam in a high-vacuum chamber with convection heat coils;and filtering the mixture of vegetable oils by a barrier filter systemto remove the remaining impurities.

Finally, it is the object of the invention to offer an electricalapparatus using a vegetable dielectric fluid containing of 60% to 80% inweight of mono-unsaturated fatty acid; of 2% to 23% in weight ofdi-mono-unsaturated fatty acid; of 0.5% to 7% in weight oftri-unsaturated fatty acid; and of 5% to 8% in weight of saturated fattyacid, wherein the dielectric fluid is free of external antioxidantcompounds and having the properties of a dielectric strength of 40 kV to70 kV at a separation of 2 mm, a dielectric constant of 2.5 to 3.1 at25° C., a dissipation factor of 0.05% to 0.15% at 25° C., a viscosityless than 50 cSt at 40° C., an acid number less than 0.06 mg KOH/g, apour point temperature of at least −18° C., and an ignition temperatureof at least 300° C.

DETAILED DESCRIPTION OF THE INVENTION

The characteristic details of the invention are described in thefollowing paragraphs, with the aim to define the invention, but withoutlimiting the scope of it.

The vegetable dielectric oil of the present invention is a novelalternative of a dielectric fluid for applications in the electricalindustry, with as a characteristic that it is free of externalantioxidants in its composition. The term “free of externalantioxidants” means, in the context of this description, that nosubstance or natural or synthetic compound has been added that improvesthe oxidative characteristics of the original composition of the crudevegetable oil to be processed, nor this substance or any compound isadded during the process of refining the vegetable oil, nor is it added,neither requires to be added to the final composition of vegetable oilto be used in the dielectric fluid composition according to thisinvention.

The dielectric fluid composition according to the invention shows acombination of vegetable oils which that in turn may consist of multiplecomponents.

In general, the vegetable oils are triglyceride compounds with a varietyof fatty acids, which differ in the number of carbon atoms in themolecules (string length), the number of double bonds in the chain(degree of saturation), position of double bonds in the chain and thegeometry of each bond. Fatty acids are organic acids (carboxylic acid)with a long molecular chain of more than 12 carbons, which can besaturated or unsaturated. Most saturated fatty acids are solid at roomtemperature, while the nature of unsaturated acids (mono-unsaturated orpoly-unsaturated) are usually liquids.

In general, unsaturated fatty acids, which contain one(mono-unsaturated) or more double bonds (poly-unsaturated), are the maincauses of oxidative reactions in vegetable oils because the double bondsare highly susceptible to the attack of oxygen. Because of the former,it is preferable that vegetable oils for electrical appliances presenthigh contents of mono-unsaturated fatty acids, and preferably fattyacids that are of the oleic type (C18:1) since they are more stable tooxidation at room temperature as well as at elevated temperatures.

In accordance with the present invention, the composition of the vegetaldielectric fluid shows characteristics suitable for its use inelectrical apparatuses without the need to add antioxidants or any otherexternal synthetic additive. The former is achieved through theincorporation of vegetable oils with high oleic acid content, as well asthe mixture with other vegetable oils.

Vegetable oils that constitute the dielectric fluid of this inventionare described individually below, without necessarily being described inan order of importance.

High Oleic Vegetable Oils

The dielectric fluid composition of this invention can make use of oilof low erucic rape seeds of the Brassica napus species, oil of higholeic safflower seeds of the Carthamus tinctorius species, oil of higholeic sunflower seeds of the Helianthus annuus species, and combinationsthereof.

Low erucic rapeseed oil presents good characteristics because of itsnatural composition, formed by a very high percentage of oleic fattyacid. This oil comes from the seeds obtained of the varieties of turnipwith a low erucic acid contents (Brassica napus). It is obtained bymechanical extraction and/or solvents. It excels by its low content ofsaturated fatty acids.

In terms of fatty acids, the composition of the high oleic rapeseed oilthat can be used in the invention is as follows:

-   -   of 52% to 67% in weight of mono-unsaturated fatty acid;    -   of 16% to 25% in weight of di-unsaturated fatty acid;    -   of 6% to 14% in weight of tri-unsaturated fatty acid, and    -   of 4.4% to 8.5% in weight of saturated fatty acid.

In terms of fatty acid components, the composition of high oleicrapeseed oil used in the invention is as follows:

-   -   of 52% to 67% in weight of oleic acid (C18:1);    -   of 16% to 25% in weight of linoleic acid (C18:2);    -   of 6% to 14% in weight of linolenic acid (C18:3);    -   of 3.3% to 6% in weight of palmitic acid (C16:0); and    -   of 1.1° A) to 2.5% in weight of stearic acid (C18:0).

The high oleic safflower oil comes from a natural genetic variety ofsafflower, whose fatty acid composition is different from thetraditional one. It contains a high level of mono-unsaturated acid(oleic acid). It is very stable and has a light yellow color.

In terms of fatty acids, the composition of the high oleic safflower oilused in the invention is as follows:

-   -   of 74% to 80% in weight of mono-unsaturated fatty acid;    -   of 13% to 20% in weight of di-unsaturated fatty acid;    -   of 6% to 14% in weight of tri-unsaturated fatty acid; and    -   of 6.5% to 8.5% in weight of saturated fatty acid.

In terms of fatty acid components, the composition of high oleicsafflower oil used in the invention is as follows:

-   -   of 74% to 80% in weight of oleic acid (C18:1);    -   of 13% to 20% in weight of linoleic acid (C18:2);    -   of 6% to 14% in weight of linolenic acid (C18:3);    -   of 5% to 6% in weight of palmitic acid (C16:0); and    -   of 1.5% to 2.5% in weight of stearic acid (C18:0).

In terms of fatty acids, the composition of the high oleic sunflower oilused in the invention is as follows:

-   -   of 74% to 88% in weight of mono-unsaturated fatty acid;    -   of 1% to 8% in weight of di-unsaturated fatty acid;    -   of 0.5% to 2% in weight of tri-unsaturated fatty acid, and    -   of 5% to 9% in weight of saturated fatty acid.

In terms of fatty acid components, the composition of high oleicsunflower oil used in the invention is as follows:

-   -   of 74% to 88% in weight of oleic acid (C18:1);    -   of 1% to 8% in weight of linoleic acid (C18:2);    -   of 0.5% to 2% in weight of linolenic acid (C18:3);    -   of 3% to 5% in weight of palmitic acid (C16:0); and    -   of 2% to 4% in weight of stearic acid (C18:0).

GRAPE SEED OIL

The grape seed oil used in the invention is a vegetable oil derived fromthe seeds of grapes of the Vitis species or its varieties.

The grape seed oil presents good dielectric characteristics, mainly itsproperty of dielectric strength. This oil is incorporated into thecomposition of this invention to improve said dielectric property.

In terms of fatty acids, the composition of grape seed oil used in thisinvention is as follows:

-   -   of 12% to 29.2% in weight of mono-unsaturated fatty acid;    -   of 58% to 78% in weight of di-unsaturated fatty acid;    -   from trace amount to 1% in weight of tri-unsaturated fatty acid;        and    -   of 8.5% to 19.5% in weight of saturated fatty acid.

In terms of fatty acids, the composition of grape seed oil used in thisinvention is as follows:

-   -   of 12% to 28% in weight of oleic acid (C18:1);    -   from trace amount to 1.2% in weight of palmitoleic acid (C16:1);    -   of 58% to 78% in weight of linoleic acid (C18:2);    -   from trace amount to 1% in weight of linolenic acid (C18:3);    -   from trace amount to 0.5% in weight of lauric acid (C12:0);    -   from trace amount to 0.3% in weight of myristic acid (C14:0);    -   of 5.5% to 11% in weight of palmitic acid (C16:0);    -   of 3% to 6% in weight of stearic acid (C18:0);    -   from trace amount to 1% in weight of arachidic acid (C20:0);    -   from trace amount to 0.3% in weight of behenic acid (C22:0); and    -   from trace amount to 0.4% in weight of lignoceric acid (C24:0).

The grape seed oil, moreover, contains natural antioxidants such aspolyphenols, including proanthocyanidins.

SESAME SEED OIL

The sesame seed oil used in this invention is a vegetable oil derivedfrom the seeds of sesame of the Sesamum indicum species.

In terms of fatty acids, the composition of sesame seed oil used in thisinvention is as follows:

-   -   of 33.6% to 44.6% in weight of mono-unsaturated fatty acid;    -   of 40.3% to 50.8% in weight of di-unsaturated fatty acid;    -   of 0.3% to 0.7% in weight of tri-unsaturated fatty acid; and    -   of 12.6% to 18.3% in weight of saturated fatty acid.

In terms of the components of fatty acids, the composition of sesameseed oil used in this invention is as follows:

-   -   of 33.5% to 44.1% in weight of oleic acid (C18:1);    -   of 0.1° A) to 0.2% in weight of palmitoleic acid (C16:1);    -   from trace amount to 0.3% in weight of gadoleic acid (C20:1);    -   of 40.3% to 50.8% in weight of linoleic acid (C18:2);    -   of 0.3% to 0.7% in weight of linolenic acid (C18:3);    -   from trace amount to 0.1% in weight of myristic acid (C14:0);    -   of 7.9% to 10.2% in weight of palmitic acid (C16:0);    -   of 4.4% to 6.7% in weight of stearic acid (C18:0);    -   of 0.3% to 0.7% in weight of arachidic acid (C20:0);    -   from trace amount to 0.3% in weight of behenic acid (C22:0); and    -   from trace amount to 0.3% in weight of lignoceric acid (C24:0).

Other components of the sesame seed oil are its antioxidants, whichbelong to the family of the lignans. Among them, there are: sesamin,sesamolin, sesamol, sesaminol, sesamolina, sesamolinol and pinoresinol.These phenolic compounds bring stability to the fatty acids present inthe dielectric fluid composition of the invention.

The presence of free radicals in the sesamol and sesamolin, causes anycontaminant present in a transformer (water, corrosion, heavy metals,etc.) to be trapped by these radicals, avoiding thus any loss of theproperties of the dielectric fluid of the present invention.

RICE BRAN OIL

The rice bran oil used in the invention is a vegetable oil derived fromrice bran of the Oryza sativa species.

In terms of fatty acids, the composition of rice bran oil used in theinvention is as follows:

-   -   of 38.3% to 49% in weight of mono-unsaturated fatty acid;    -   of 16% to 36% in weight of di-unsaturated fatty acid;    -   of 0.2% to 2.2% in weight of tri-unsaturated fatty acid; and    -   of 18.5% to 34.5% in weight of saturated fatty acid.

In terms of fatty acids, the composition of rice bran oil used in theinvention is as follows:

-   -   of 38% to 48% in weight of oleic acid (C18:1);    -   from trace amount to 0.5% in weight of palmitoleic acid (C16:1);    -   of 0.3% to 0.5% in weight of gadoleic acid (C20:1);    -   of 16% to 36% in weight of linoleic acid (C18:2);    -   of 0.2% to 2.2% in weight of linolenic acid (C18:3);    -   of 0.5% to 0.7% in weight of myristic acid (C14:0);    -   of 16% to 28% in weight of palmitic acid (C16:0);    -   of 2% to 4% in weight of stearic acid (C18:0);    -   of 0.5% to 0.8% in weight of arachidic acid (C20:0);    -   of 0.1% to 0.5% in weight of behenic acid (C22:0); and    -   from trace amount to 0.5% in weight of lignoceric acid (C24:0).

Other components of rice bran oil are its natural antioxidants, mainlythe so-called gamma-orizanol, which is present in a range of 1% to 2% inweight, and which is a ferulic acid ester of triterpenic alcohols. Thiscompound brings stability to the fatty acids present in the dielectricfluid composition of the invention.

PREPARATION MODE, MIXTURE, PROCESS, AND COMPOSITION OF THE DIELECTRICFLUID OF THE INVENTION

The process to produce the dielectric fluid of the invention starts withthe preparation of a crude high oleic vegetable oil mixture, crude grapeseed oil, crude sesame seed oil, and crude rice bran oil, combining thefollowing quantities:

-   -   of 95.5% to 99.25% in weight of at least one high oleic        vegetable oil;    -   of 0.25% to 1.5% in weight of grape seed oil;    -   of 0.25% to 1.5% in weight of sesame seed oil; and    -   of 0.25% to 1.5% in weight of rice bran oil.

Once the mixture of crude vegetable oils is prepared, it is subjected toa physical refining process, completely natural and without the help ofsynthetic agents or external antioxidants, which allows the dielectricfluid of the invention to be kept completely natural and free ofexternal antioxidants.

The physical refining process of the invention consists of the steps ofdegumming, distillation, deodorization, filtering, winterizing, andpolishing. It is very important to mention that through this process ofphysical refining, chemicals agents are excluded, used in traditionalrefining processes (process RBD), such as organic solvents, oxidantagents for neutralization, inorganic acids for degumming, inert gases toprevent oxidation, addition of synthetic antioxidants to improve theshelf life, among others.

Each of these steps is described below.

Degumming

In the step of degumming, the hydrophibic phospholipids andnon-hydrophobics are removed from the crude vegetable oil by adding foodgrade citric acid within a temperature-controlled reactor of less than50° C. The reactor is connected to a vacuum system (300 mmHg.) thatprevents the oxidation of the oil and the phospholipids. After thereaction, the hydrophobic phospholipids by density decant and thenon-hydrophobics form a cream, with the control product remaining inbetween both. A system of centrifugal force is responsible for theseparation by densities.

Distillation

Once the vegetable oil is degummed, continue to the step ofdistillation. In this step, the fatty acid triglycerides in the form offree radicals, better known as free fatty acid (FFA) are distilled inhigh vacuum, that is, they are not neutralized as is commonly done in atraditional refining process of the RBD type.

Desodorization

Once the oil is distillated, deodorization of the oil is continued, byhigh-vacuum chambers (from 0 mmHg to 6 mmHg) with convection heatingcoils to achieve a temperature of 250° C., without burning the oil,because in the absence of oxygen, no combustion or polymerizationreaction is generated. At this step, the oil is stirred directly withdry steam with the aim of causing a drag on the most hidden impuritiesmolecules contained until now in the oil, achieving with this a finishedoil, without color, nor peroxide, acid-free, odorless and without gums.

At this step of deodorization, by a drag system of distilled vapors thatcontain the impurities from the oil, such as acid chains of freeradicals, smells, tastes, pigments and peroxides. This is accomplishedthrough a packed bed working under a constant bath of free fatty acids,which allow dissolving the impurities from the vapors that leave towardsthe vacuum system. This collection system allows the complete separationof these impurities from the oil.

FILTRATION

Once the oil is deodorized, any remaining impurities are separated byfiltration from the oil, for example, the pigments that are absorbed.Therefore, the deodorized oil is passed through a barrier filter systemof approximately 5 microns opening.

WINTERIZING

Once the oil is filtered, then it is proceeded to extract the waxcontained therein through a cold chamber, which is to cool the filteredoil at a temperature of 0° C. to 5° C. with the aim to encourage theformation of waxes that by density decant in the bottom part of thecontainer. This avoids the turbidity of the oil when stored at lowtemperatures thus improving the pour point temperature.

POLISHING

As an alternative, once the oil has been winterized, it is proceeded,through a multiple filtering system to separate the oil waxes, giving aterminal brightness, translucency and crystalline.

In terms of fatty acids, the composition of the dielectric fluid of theinvention, once physically refined, is as follows:

-   -   of 60% to 80% in weight of mono-unsaturated fatty acid;    -   of 2% to 23% in weight of di-unsaturated fatty acid;    -   of 0.5% to 7% in weight of tri-unsaturated fatty acid; and    -   of 5% to 8% in weight of saturated fatty acid;

In terms of the components of fatty acids, the composition of thedielectric fluid of this invention is as follows:

-   -   of 60% to 80% in weight of oleic acid (C18:1);    -   of 2% to 23% in weight of linoleic acid (C18:2);    -   of 0.5% to 7% in weight of linolenic acid (C18:3);    -   of 3% to 5% in weight of palmitic acid (C16:0); and    -   of 2% to 3% in weight of stearic acid (C18:0).

In one particular implementation, using low erucic rapeseed oil in thecomposition of the dielectric fluid of the invention, in terms of fattyacid components, these are as follows:

-   -   of 60% to 63% in weight of mono-unsaturated fatty acid;    -   of 20% to 23% in weight of di-unsaturated fatty acid;    -   of 5% to 7% in weight of tri-unsaturated fatty acid; and    -   of 6% to 8% in weight of saturated fatty acid.

In this particular embodiment, the composition of the dielectric fluidof this invention is as follows:

-   -   of 60% to 63% in weight of oleic acid;    -   of 20% to 23% in weight of linoleic acid;    -   of 5% to 7% in weight of linolenic acid;    -   of 4% to 5% in weight of palmitic acid; and    -   of 2% to 3% in weight of stearic acid.

The levels of impurities of the dielectric fluid composition of thisinvention, determined by the Official methods of the American OilChemists' Society (AOCS) are the following:

-   -   less than 0.05% in weight of free fatty acids under the AOCS Ca        5a-40 method; 0 ppm of soap under the AOCS Cd 17-95 method; and        less than 2 meq/kg of peroxid index.

Physical Properties of the Composition of the Dielectric Fluid of theInvention

The dielectric fluid composition of the invention has specific physicalproperties that make them particularly suited for use as a fluid forelectrical insulation, said properties being:

-   -   a dielectric strength of 40 kV to 70 kV at a separation of 2 mm        and preferably of 40 kV to 55 kV at a separation of 2 mm;    -   a dielectric constant of 2.5 to 3.1 at 25° C.;    -   a dissipation factor of 0.05% to 0.15% at 25° C. and preferably        of 0.06% to 0.1% at 25° C.;    -   a viscosity less than 50 cSt at 40° C.;    -   an acid number less than 0.6 mg KOH/g;    -   a pour point temperature of −18° C. to −10° C. and preferably of        −15° C. to −12° C.; and    -   an ignition temperature of at least 300° C.

The dielectric strength, the dielectric constant, the dissipationfactor, the pour point temperature and the acid number are measuredusing each test methods of the American Society for Testing andMaterials (ASTM). The dielectric strength is determined using the testmethod ASTM D1816. The dielectric constant is determined using the testmethod ASTM D924. The dissipation factor is determined using the testmethod ASTM D924. The viscosity is determined using standard ASTM D445.The pour point temperature is determined using the test method ASTM D97.The acid number is determined using the test method ASTM D974.

In some embodiments, the pour point temperature or flow point of thedielectric fluid of the invention can be further reduced by prolongingits cooling time. Essentially, the obtained dielectric fluid is cooledor frozen by decreasing the temperature to near or below 0° C. for aperiod of approximately 72 hours and removing the solidified components.The stage of cooling or freezing can be performed as a series ofreductions in temperature followed by the removal of solids at saidtemperatures.

EXAMPLES OF EMBODIMENT OF INVENTION

The invention will now be described with respect to the followingexamples, which are solely for the purpose of representing the way ofcarrying out the implementation of the principles of the invention. Thefollowing examples are not intended to be a comprehensive representationof the invention, nor try to limit the scope of it.

Table 1 shows examples of dielectric fluid compositions according to theinvention.

TABLE 1 Component Example 1 Example 2 Example 3 % in weight of lowerucic 98.5 97 95.5 rapeseed oil % in weight of grape seed 0.5 1 1.5 oil% in weight of sesame seed 0.5 1 1.5 oil % in weight of rice bran oil0.5 1 1.5

Table 2 illustrates the physical properties obtained for each of theexamples in Table 1.

TABLE 2 Physical properties Example 1 Example 2 Example 3 Dielectricstrength (kV) 60 47.4 47.6 25° C. at 2 mm, ASTM D1816 Dielectricconstant 2.6 2.5 2.6 at 25° C. ASTM D924 Dissipation factor 0.114 0.1160.114 at 25° C. ASTM D924 Pour point temperature (° C.) −15 −15 −15 ASTMD97 Acid number 0.051 0.053 0.053 (mg KOH/gr) ASTM D974 Viscosity (cSt)at 40° C. 38 43 41

The dielectric fluid composition according to the invention is a naturalcomposition based on the mixture of vegetable oils, free of externalantioxidants and complies with the current requirements andspecifications for plant-type dielectric fluids, making feasible itsimplementation in electrical appliances, including electricaltransformers, capacitors or transmission cables. Unlike the currentdielectric vegetable oils, to which synthetic compounds areincorporated, this invention provides a composition free of externalantioxidants whether natural, synthetic or mixtures thereof in itsformulation, obtaining the final characteristics through a physicalrefining process. The result is a completely natural dielectric fluid,highly biodegradable, such characteristics that allow minimizing to themaximum a negative impact on the environment, for any fluid spillaccidents, generation of toxic wastes and fire hazards.

Finally, it should be understood that the dielectric fluid compositionbased on a mixture of vegetable oils and free of external antioxidantsand the method for obtaining it from the present invention are notlimited to the mode or modes described above and that experts in thefield are trained herein, for the teachings that are shown herein, tomake changes in the composition of the dielectric fluid free of externalantioxidants and the method for obtaining it of the present invention,whose scope is established exclusively for the following claims:

1-37. (canceled)
 38. An electric apparatus comprising a dielectric fluidincluding: from 95.5% to 99.25% by weight of at least one oleicvegetable oil selected from a group of consisting of low erucic rapeseedoil, high oleic sunflower oil, high oleic safflower oil, andcombinations thereof; from 0.25% to 1.5% by weight of grape seed oil;from 0.25% to 1.5% by weight of sesame seed oil; and from 0.25% to 1.5%by weight of rice bran oil; wherein said dielectric fluid is free ofexternal antioxidants and has: a dielectric strength of 40 kV to 70 kVat a separation of 2 mm; a dielectric constant of 2.5 to 3.1 at 25° C.;and a dissipation factor of 0.05% to 0.15% at 25° C.
 39. The electricapparatus of claim 38, wherein the dielectric fluid has a dielectricstrength of 40 kV to 55 kV at a separation of 2 mm.
 40. The electricapparatus of claim 38, wherein the dielectric fluid has a dissipationfactor of 0.06% to 0.1% at 25° C.
 41. The electric apparatus of claim38, wherein the dielectric fluid has: a viscosity less than 50 cSt at40° C.; a pour point temperature of −18° C. to −10° C.; an acid numberless than 0.06 to 0.1 mg KOH/g; and an flash point temperature of atleast 300° C.
 42. The electric apparatus of claim 41, wherein thedielectric fluid has a pour point temperature of −15° C. to −12° C. 43.The electric apparatus of claim 38, wherein the dielectric fluid has:less than 0.05% by weight of free fatty acids; 0 ppm of soap; and lessthan 2 meq/kg of peroxid index.
 44. The electric apparatus of claim 38,wherein, in terms of fatty acids, the dielectric fluid comprises: from60% to 80% by weight of oleic acid; from 2% to 23% by weight of linoleicacid; from 0.5% to 7% by weight of linolenic acid; from 3% to 5% byweight of palmitic acid; and from 2% to 3% by weight of stearic acid.45. The electric apparatus of claim 38, wherein, in terms of fattyacids, the dielectric fluid comprises: from 60% to
 634. 80% by weight ofmono-unsaturated fatty acid; from
 20170. 2% to 23% by weight ofdi-unsaturated fatty acid; from
 54. 0.5% to 7% by weight oftri-unsaturated fatty acid; and from 6 5% to 8% by weight of saturatedfatty acid.
 46. The electric apparatus of claim 44, wherein thedielectric fluid comprises: from 60% to 63% by weight of oleic acid;from 20% to 23% by weight of linoleic acid; from 5% to 7% by weight oflinolenic acid; from 4% to 5% by weight of palmitic acid; and from 2% to3% by weight of stearic acid.
 47. (canceled)
 48. (canceled)
 49. Theelectric apparatus of claim 38, wherein the low erucic rapeseed oil isoil of low erucic rape seeds of Brassica napus species.
 50. The electricapparatus of claim 38, wherein the high oleic safflower oil is oil ofhigh oleic safflower seeds of Carthamus tinctorius species.
 51. Theelectric apparatus of claim 38, wherein the high oleic sunflower oil isoil of high oleic sunflower seeds of Helianthus annuus species.
 52. Theelectric apparatus of claim 38, wherein the grape seed oil is oil ofgrape seed of Vitis species.
 53. The electric apparatus of claim 38,wherein the sesame seed oil is oil of sesame seeds of Sesamum indicumspecies.
 54. The electric apparatus of claim 38, wherein the rice branoil is oil of rice bran of Oryza sativa species.